Revisiting the laser dye Styryl-13 as a reference near-infrared fluorophore: implications for the photoluminescence quantum yields of semiconducting single-walled carbon nanotubes.

The near-infrared (NIR) polymethine dye Styryl-13 emitting at approximately 925 nm has recently been suggested as a reference fluorophore for determining the quantum yield (QY) of the NIR photoluminescence of dispersed single-walled carbon nanotubes (SWNTs). Ju et al. reported the QY for SWNTs to be as high as 20% on the basis of 11% QY for Styryl-13 in methanol (Science 2009, 323, 1319). We directly compared the fluorescence of Styryl-13 and Styryl-20 (emitting at approximately 945 nm) with that of the standard fluorophore Rhodamine 6G using a spectrometer with a broad visible-NIR detection range. QYs of 2.0 (4.5) and 0.52 (0.80)% were determined for Styryl-13 and Styryl-20 in methanol (propylene carbonate), respectively. Correspondingly, the above-mentioned photoluminescence efficiency of SWNTs appears to be strongly overestimated. We also discuss singlet oxygen as an alternative NIR reference. A total QY of 1.4% was measured for the emission of singlet oxygen at 1275 nm, as photosensitized by C70 fullerene in air-saturated carbon tetrachloride.